An enthusiast who has spent years patching up a vintage car is bound to find it tough to admit that the vehicle can no longer be driven. The Archbishop of Canterbury, Rowan Williams, now finds himself in a similarly painful position in respect of the Anglican communion. For years he has used his considerable charm to try to hold it together. But the simmering row over homosexuality has made this increasingly difficult. And two developments in the past fortnight make brutally plain that the communion is already falling apart.

Last week primates from the developing world - led by the conservative Nigerian bishop Peter Akinola - issued a demand that the Lambeth conference planned for next year should be postponed until the disputes dividing the affiliation have been decisively settled. Their aggressive stance cuts to the heart of the communion, since the Lambeth conference, held once every 10 years, is one of the only institutional expressions of this loose allegiance of churches. Then, on Thursday, another conservative archbishop -this time based in Latin America - suggested he was ready to adopt breakaway dioceses from within the US. In making the offer Bishop Gregory Venables launched a direct attack on the American Episcopal church, which has been trying to stem a flow of conservative defectors since New Hampshire elected the openly gay Gene Robinson as a bishop in 2003. By definition, in an "episcopal" church individual bishops hold sway in specific areas. If another bishop is competing for worshippers then he is running a different and parallel church.

Always a loose and unwieldy alliance, the communion has survived since the age of empire only because of the effective acceptance that each church was sovereign in its own land. With the initial encouragement of the religious right in America, however, conservative elements of the communion are trying to impose an infeasible doctrinal unity. Dr Williams has responded to this pressure by seeking compromises. His difficulty is that, as the head of such a loose confederation, he does not have the power to make deals stick, as the freewheeling action of the conservatives is showing.

Dr Williams is a liberal who is instinctively supportive of gay people. His desire to hold the communion together, however, has already led him to support a moratorium on the consecration of gay bishops and to suggest that Anglican churches should not recognise same-sex unions through public rites. These concessions have not, however, checked the communion's unravelling. The fence on which Dr Williams has been sitting has collapsed. It is time for him to preach what he believes.